In the fields of authenticating of physical articles it is known to rely upon an identifier for the article. An identifier based on a physical property may be used, these can include embedded reflective particles (WO02/50790A1, U.S. Pat. No. 6,584,214) or an unmodified surface of the article (WO2005/088533). The inventor's previous work in this field has related to determining an identifier from an unmodified surface of an article by illuminating the surface with a coherent light beam. Others (WO2006/021083) have proposed the use of an LED source for presenting a stimulus to a target, both with a modified article and an unmodified article. However, the arrangements proposed in WO2006/021083 are extremely difficult to use to create a useful device with high authentication reliability.
To provide an authentication result based upon such an identifier, it is necessary to compare a reading from the article to be authenticated to a stored reading result. For this comparison, a match finding algorithm is used.
The present invention has been conceived in the light of known drawbacks of existing systems.